In wireless packet data systems, such as Enhanced General Packet Radio Service (EGPRS) and Universal Mobile Telecommunication System (UTMS), a form of selective repeat automatic repeat request (ARQ) referred to as radio link control (RLC), or alternatively, radio link protocol (RLP), is used to reduce the packet loss rate seen by end-to-end applications by link layer retransmissions. The improvement in packet loss rate comes at the expense of increased delay and reduced link throughput due to retransmissions.
Higher layer data packets are segmented into RLC (or RLP) blocks depending on the modulation and coding scheme (MCS) used. RLC blocks are transmitted via the wireless channel to a receiving terminal. The receiving terminal replies with an acknowledgement (ACK) if the block was properly received or negative acknowledgement (NACK) if the block was received in error or not received. The NACK acts as a request to retransmit any blocks that were not received or received in error. Most RLC/RLP error recovery systems, such as used in EGPRS, are infinitely persistent, that is, there is no limit on the number of re-transmit attempts for a given block. Some systems are moderately persistent and limit the number of retransmission attempts. For example, with respect to RLP in code division multiple access (CDMA) systems using Telecommunications Industry Association (TIA) IS-2000, a receiving terminal simply drops a block if it is not correctly received after requesting NACKs 5 times. In another example, according to RLC for UTMS, after a retransmit count is exceeded at the transmitting terminal, if the block is still not received at the receiving terminal, the transmitting terminal drops the block and signals to the receiving terminal to move its receive window accordingly.
There are, however, an increasing number of applications that may prefer a higher packet loss at lower delay. For example, streaming voice/audio/data applications, push-to-talk (PTT), voice over Internet Protocol (VoIP) are all concerned with packet delay. Currently known infinitely persistent methods are not well suited to such applications. Likewise, known moderately persistent methods may not provide the desired quality of service (QoS) trade-off between delay and packet loss.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.